It is known that homopolymers or copolymers obtained from a fumaric diester show high heat resistance as compared with general thermoplastic vinyl polymers, and further give a resin having excellent transparency. For example, a homopolymer obtained from diisopropyl fumarate or dicyclohexyl fumarate does not show its softening point or glass transition temperature even at a temperature of 200° C. or higher, and therefore is a promising material as a transparent resin usable in various applications in an optical field (see, for example, Patent Document 1 or Non-Patent Document 1)
[Patent Document 1]: JP-B-5-40281 (The term “JP-B” used herein means an “examined Japanese patent publication”)
[Non-Patent Document 1]: Takayuki Otsu, Mirai Zairyo (Feature Materials), 2002, Vol. 2, No. 12 (pp 70-74)
However, Patent Document 1 and Non-Patent Document 1 do not describe a copolymer comprising a fumaric diester residue unit, and a (meth)acrylic ester residue unit having an oxetanyl group and/or a (meth)acrylic ester residue unit having a tetrahydrofurfuryl group.